In order to drive a vehicle, a hybrid drive system provided with an engine and a motor has been proposed by Japanese Patent Laid-Open Publications No. 10-304513 and No. 2001-103603.
In addition, it is known that a clutch is interposed between an engine and a transmission and a rotating electric machine having functions of an electric motor and an electric generator is coupled to an input side of the transmission.
In such a hybrid system, an inertia force caused by the rotating electric machine connected to an input shaft of the transmission is applied at the time of the gear shift of the transmission and therefore, synchronization of rotation needs longer time, thus increasing time required for the gear shift.